4-Chloro-pyridine-2,6-dicarboxylic acid

499-51-4

4722-94-5

4-Hydroxy-2,6-pyridinedicarboxylic acid (43.76 g, 0.218 mol) and phenylphosphonic dichloride (122 mL, 0.87 mol) were added to a 500 mL three-necked round-bottomed flask fitted with a reflux condenser and a calcium chloride desiccant tube under nitrogen protection. The resulting suspension was heated in an oil bath to 75°C, at which point the reaction mixture became violently exothermic and foam was generated. The foam was controlled by adjusting the heating rate and by passing nitrogen into the foam. After the reaction stabilized, the temperature was slowly increased to 130°C with continuous stirring for 3 hours. Upon completion of the reaction, the slightly red mixture was cooled to about 50°C and subsequently slowly poured into 500 mL of deionized water with stirring. The temperature of the water increased during the hydrolysis process. The deionized water was replenished to a total of 800 mL to ensure complete transfer. The resulting cream-colored solid was heated and stirred at 40-50°C for 1 hour, followed by slow cooling to room temperature and stirring overnight. The precipitate was collected by diafiltration, washed with excess deionized water and air dried. Preliminary 1H NMR (d6-DMSO) analysis showed phenylphosphonic acid mixed in the product. For purification, the solid was dissolved in 500 mL of deionized water, stirred at 55°C for 30 min and then diafiltrated, washed with water and air-dried to give the pure product (43.9 g). The 1H NMR (d6-DMSO) of the purified product showed a single peak (8.24 ppm). The results of elemental analysis were consistent with the theoretical values (C7H4ClNO4-0.8H2O): calculated values C 38.93%, H 2.71%, N 6.49%, Cl 16.42%; measured values C 38.8%, H 2.88%, N 6.23%, Cl 16.72%.